Arterial pressure waveform analysis versus thermodilution cardiac output measurement during open abdominal aortic aneurysm repair

BACKGROUND: Arterial pressure waveform analysis enables continuous, minimally invasive measurement of cardiac output. Haemodynamic instability compromises the reliability of the technique and a means of maintaining accurate measurement in this circumstance would be useful. OBJECTIVES: To investigate the accuracy, precision and trending ability of arterial pressure waveform cardiac output obtained with FloTrac/Vigileo, versus pulmonary artery thermodilution in patients undergoing elective open abdominal aortic aneurysm repair. DESIGN: A prospective observational study. SETTING: Operating room in a university hospital. PATIENTS: Twenty-two patients scheduled for elective, open abdominal aortic aneurysm repair. MAIN OUTCOME MEASURES: Bias, limits of agreement and mean error as determined with Bland-Altman analysis between arterial waveform and thermodilution cardiac output assessment at four time points: after induction of anaesthesia (t1); after aortic cross-clamping (t2); after clamp release (t3); and after skin closure (t4). Trending ability from t1 to t2, t2 to t3 and t3 to t4, determined with four-quadrant and polar plot methodology. Clinically acceptable boundaries were defined in advance. RESULTS: Bland-Altman analysis revealed a bias of 0.54 l min (thermodilution minus arterial waveform cardiac output) for pooled data, and 0.51 (t1), -0.42 (t2), 0.98 (t3) and 0.98 (t4) l min at the different time points. Limits of agreement (LOA) were [-3.0 to 4.0] (pooled), [-2.0 to 3.0] (t1), [-3.1 to 2.3] (t2), [-2.5 to 4.4] (t3) and [-1.7 to 3.7] (t4) l min, resulting in mean errors of 58% (pooled), 45% (t1), 53% (t2), 52% (t3) and 41% (t4). Four-quadrant concordance was 65%. Polar plot analysis resulted in an angular bias of -12°, with radial LOA of -60° to 36°. CONCLUSION: Bias between arterial waveform and thermodilution cardiac output was within a predefined acceptable range, but the mean error was above the accepted range of 30%. Trending ability was poor. Arterial waveform and thermodilution cardiac outputs are, therefore, not interchangeable in patients undergoing open abdominal aortic aneurysm repair.